AP7335

300mA, Low Quiescent Current, Fast Transient

Low Dropout Linear Regulator

AP7335

Document number: DS32259 Rev. 2 - 2

11 of 17

www.diodes.com

September 2010

© Diodes Incorporated

Application Note

Input Capacitor

A 1

μF ceramic capacitor is recommended between IN and

GND pins to decouple input power supply glitch and noise.

The amount of the capacitance may be increased without

limit. This input capacitor must be located as close as

possible to the device to assure input stability and reduce

noise. For PCB layout, a wide copper trace is required for

both IN and GND pins. A lower ESR capacitor type allows

the use of less capacitance, while higher ESR type

requires more capacitance.

Output Capacitor

The output capacitor is required to stabilize and improve

the transient response of the LDO. The AP7335 is stable

with very small ceramic output capacitors. Using a ceramic

capacitor value that is at least 1

μF with ESR > 15mΩ on

the output ensures stability. Higher capacitance values

help to improve line and load transient response. The

output capacitance may be increased to keep low

undershoot and overshoot. Output capacitor must be

placed as close as possible to OUT and GND pins.

0.001

0.01

0.1

1

10

100

0

50

100

150

200

250

300

Load Current (mA)

Adjustable Operation

The AP7335 provides output voltage from 0.8V to 5.0V

through external resistor divider as shown below.

1u F

IN

GN D

EN

OU T

En a b le

AD J

R2

R1

1u F

A P 7335

The output voltage is calculated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+

=

2

R

1

R

1

REF

V

OUT

V

Rearranging the equation will give the following that is

used for adjusting the output to a particular voltage:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

=

1

REF

V

OUT

V

2

R

1

R

To maintain the stability of the internal reference voltage,

No Load Stability

Other than external resistor divider, no minimum load is

required to keep the device stable. The device will remain

stable and regulated in no load condition.

ON/OFF Input Operation

The AP7335 is turned on by setting the EN pin high, and is

turned off by pulling it low. If this feature is not used, the

EN pin should be tied to IN pin to keep the regulator

output on at all time. To ensure proper operation, the

signal source used to drive the EN pin must be able to

swing above and below the specified turn-on/off voltage

thresholds listed in the Electrical Characteristics section

Current Limit Protection

When output current at OUT pin is higher than current limit

threshold, the current limit protection will be triggered and

clamp the output current to approximately 600mA to

prevent over-current and to protect the regulator from

damage due to overheating.

Short Circuit Protection

When OUT pin is short-circuit to GND, short circuit

protection will be triggered and clamp the output current to

approximately 140mA. This feature protects the regulator

from over-current and damage due to overheating.

Thermal Shutdown Protection

Thermal protection disables the output when the junction

temperature rises to approximately +145°C, allowing the

device to cool down. When the junction temperature

reduces to approximately +130°C the output circuitry is

enabled

again.

Depending

on

power

dissipation,

thermal resistance,

and

ambient

temperature,

the

thermal protection

circuit

may

cycle

on

and

off.

This cycling limits the heat dissipation of the regulator,

protecting

it from damage

due

to

overheating.

Unstable Range

Stable

R

Unstable Range